1. Field of the Invention
The present invention relates to water-degradable carrier-filler materials and more particularly to the production of such materials from phosphatic clays which are normally discarded as a waste material by phosphate mining operations. While the granular carrier-filler material is primarily useful as a component of granular fertilizers and insecticides, it also has utility as an absorbent material and as a base for manufactured cat litter.
2. Description of the Prior Art
The use of carrier-filler materials in granular fertilizers and insecticides is certainly well known in the prior art. For example, for many years materials such as sand, crushed stone, coal slag, gravel and rocks have been used as excipients in the manufacture of nonliquid granular fertilizers and insecticides. However, such prior art carrier-filler materials possess inherent undesirable characteristics. For example, most such materials are not water-degradable; they generally provide no additional mineral nutrients; and they generally do not function as soil conditioners. Nevertheless, in order to provide commercially feasible granular fertilizers and insecticides such excipients must be utilized for the purpose of adding weight and bulk to the various combinations of ingredients necessary to achieve the desired proportions of such ingredients in a fixed unit of measure.
Because of the source material utilized in practicing this invention, namely phosphatic clays, any discussion of pertinent prior art must also consider the phosphate industry as it is presently conducted for the production of fertilizers. Phosphate rock ore, called matrix, is mined to produce phosphate materials of suitable purity and form for use as fertilizers, human and animal food product supplements, and other general chemical applications. Referring specifically to the Bone Valley formation in central Florida, this is the most important source of phosphate in the United States. More than one hundred million tons of phosphate ore are being mined annually in that area. As is well known in the phosphate industry, approximately one-third (1/3) of the total matrix mined is discarded as undesirable waste phosphatic clays which consist primarily of finely divided clay particles suspended in water and possessing properties that prevent effective settling. The high volume and extremely slow settling of the phosphatic clays requires that large land areas be devoted to massive settling ponds or basins for extended periods without any further productive use. This relatively inefficient land use, coupled with the loss of water and phosphate values contained in the suspended phosphatic clays, provides a high degree of motivation within both the government and the phosphate industry to develop a practical, cost-effective solution to the problem of phosphatic clay disposal.
Thusfar numerous individuals and organizations, including the U.S. Bureau of Mines, have studied the problem and failed to develop a practical, cost-effective solution. For example, U.S. Pat. No. 2,569,323 to Maynard discloses a method of applying a process known as "bloating" to produce a lightweight aggregate suitable for construction purposes from phosphate wastes, commonly referred to as phosphate slime. Thus, the Maynard patent does teach an invention for utilizing the phosphate waste material in a productive manner. However, his method calls for extruding consolidated slimes and then firing the extrusion at temperatures of at least 1600.degree. F. to cause bloating thereof. The result of the Maynard process is the production of a hard, durable lightweight aggregate. The result of the Maynard process certainly would not be suitable as a carrier-filler material such as that of this invention for the reason that it is not water-degradable, it would not provide a secondary source of mineral nutrients, and it would not function as a soil conditioner. Furthermore, since this patent issued to Maynard in 1951, the cost of energy has increased dramatically. It seems clear that the cost of producing temperatures in excess of 1600.degree. F. would severely militate against the commercial feasibility of his method.
Other prior art patents have recognized the feasibility of producing aggregate-type materials by heating clay or similar earthy material to both expand and dry the material. U.S. Pat. No. 2,015,381 to Harding, et al., teaches a method wherein the raw material is fused at a temperature materially above 2000.degree. F. A similar bloated product is taught in U.S. Pat. No. 2,478,757 to Foster. This patent teaches the desirability of heating at temperatures of the order of 1600.degree. F. to 2200.degree. F. Similar pertinent, though clearly distinct from the present invention, teachings are presented in U.S. Pat. Nos. 1,920,773 to Walton and 1,751,163 to Loessin.
Insofar as prior art means for efficiently treating phosphatic clay wastes is concerned, Information Circular 8668 titled "The Florida Phosphate Slimes Problem" published in 1975 by U.S. Bureau of Mines, is a most thorough review and bibliography. As stated in that publication, no completely satisfactory solution has been developed. Of particular note is the fact that in the portion of the pamphlet concerning recommendations for future research, there is virtually no suggestion of any means for efficiently and economically recovering the phosphate material from the clays so that it may be put to use.
It is therefore apparent that there is a great need in the art not only for means of dealing with the efficient disposal of phosphatic clays, but also of providing an economical, water-degradable carrier-filler material useful in the fertilizer industry and possessing qualities of providing a secondary source of mineral nutrients and functioning as a soil conditioner.